Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G71/00—Macromolecular compounds obtained by reactions forming a ureide or urethane link, otherwise, than from isocyanate radicals in the main chain of the macromolecule
  • C08G71/02—Polyureas
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L75/00—Compositions of polyureas or polyurethanes; Compositions of derivatives of such polymers
  • C08L75/02—Polyureas
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/22—Electroplating: Baths therefor from solutions of zinc
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/565—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of zinc

Definitions

• the invention relates to additives for electrolyte baths for electrodeposition of a zinc or zinc alloy layer.
• the additives are polymers having terminal amino groups.
• the additives particularly effect a low formation of bubbles and few burnings as well as a uniform distribution of layer thickness during electrodeposition of zinc or zinc alloy layers.
• N,N′-Bis(dialkylaminoalkyl)urea- ⁇ , ⁇ -dihalogenalkyl copolymers have found a broad application as additives in electrodeposition baths. These compounds are particularly used as grain refiners in alkaline zinc electrolytes.
• EP 1 114 206 B1 describes a formulation consisting of N,N′-Bis(dialkylaminoalkyl)urea- ⁇ , ⁇ -dihalogenalkyl copolymers and quaternized pyridine-3-carboxylic acids and an aromatic aldehyde, which excels in that the often described formation of bubbles during zinc deposition can be avoided. Comparative experiments, however, show that a formation of bubbles occurs, in some cases after a longer period of time.
• the above-mentioned copolymers may be produced according to U.S. Pat. No. 4,157,388 by a 1:1 reaction of a N,N′-bis(dialkylaminoalkyl)urea with a ⁇ , ⁇ -dihaloalkane.
• a suitable alkylation agent such as a monohaloalkane or an acid, the polymerization can be terminated and the molecular weight distribution can be set in accordance with the desired application.
• the copolymers produced in this way often contain, in addition, an organically bound halogen, which gives, depending on the electrolyte, rise to an AOX contamination.
• an organically bound halogen which gives, depending on the electrolyte, rise to an AOX contamination.
• no mixed copolymers or oligomers containing different dihalo compounds or diamino compounds in alternating order can be produced.
• the above-mentioned (cationic) copolymers often contain halide ions as counter ions.
• thioronium compounds are often obtained at the polymerization, which have a negative influence on zinc depositions, since particularly these have a poor stability in alkaline mediums and will decompose.
• the electrolyte baths according to the invention are, in particular, to mostly yield a bubble and burning-free zinc and zinc alloy layers having a mostly uniform distribution of layer thickness and high gloss.
• X and Y each can be the same or different and represent O or NR, wherein R stands for H or C 1 -C 6 -alkyl,
• L stands for a divalent residue, which is selected from the group consisting of
• single units A may be the same or different
• single units L may be the same or different
• n represents an integer and n>0, preferably >3, more preferably >5, most preferably >10, and
• polymer chain has units A at both ends.
• R1, R2, R5 and R6 may represent, as mentioned before, a substituted or unsubstituted hydrocarbon residue having 1 to 10 carbon atoms, preferably methyl, ethyl, hydroxyethyl or —CH 2 CH 2 (OCH 2 CH 2 ) y —OH, wherein y is between 0 and 4.
• the aforementioned hydrocarbon residues can, in particular, be substituted with C 1 -C 6 alkyl (preferably —CH 3 , —CH 2 CH 3 ), aryl (preferably phenyl) or aralkyl (preferably benzyl).
• polymer has to be understood in a broad sense in connection with the present invention. It comprises any compound which has been formed by reaction of at least two monomer molecules.
• polymer does comprise, in particular, compounds which are typically designated as oligomers.
• polymer is, in connection with the present invention also applied to compounds, which are formed by a poly “condensation” reaction.
• the polymer of Formula I can be obtained by reacting one or more diamino compounds of formulae II to VII with one or more compounds of the following formula VIII, P-L-Q (VIII)
• L has the same meaning as in formula I and wherein P and Q may each be the same or different and represent halogens such as Cl, Br and I or pseudohalogens such as OMs (mesylate), OTf (triflate), ONE (nonaflate), or OTs (tosylate), and
• ratio (n A :n B ) of the total amount of substance used of the compound(s) of formulae II to VII (n A ) to the total amount of substance of the compound(s) of formula VIII (n B ) is at least 1.1:1, preferably 1.3:1, more preferably at least 1.5:1.
• the compounds of the Formula VIII are organic di(pseudo)halogen compounds.
• the di(pseudo)halogen compound of the Formula VIII is used in a substoichiometric amount with respect to component(s) of the Formula II to VII.
• the chain of the polymer of the Formula I has units A having amino groups at both ends. These terminal amino groups are at first tertiary (as in the compounds of Formulae II to VII), but may be quaternized. In acidic solution, the amino groups exist in completely or partially protonated form.
• linkages between units A and residues L occur via quaternary ammonium groups, which are formed by substitution of groups P and Q in the compounds of Formulae VIII by the tertiary amino groups of the compounds of the Formulae II to VII.
• terminal tertiary amino groups may be quaternized in accordance with the desired properties by using a organic monohalide, such as benzyl chloride, allyl chloride, alkyl chloride or their corresponding bromides, or by using an appropriate mineral acid, such as hydrochloric acid, hydrobromic acid, hydroiodic acid or sulfuric acid.
• a organic monohalide such as benzyl chloride, allyl chloride, alkyl chloride or their corresponding bromides
• an appropriate mineral acid such as hydrochloric acid, hydrobromic acid, hydroiodic acid or sulfuric acid.
• the polymer of the Formula I preferably has a molecular weight of at least 500 (g/mol).
• reaction of diamino compounds of the Formulae II to VII with the compounds of the Formula VIII may preferably be carried out in aqueous or aqueous-alcoholic, respectively, solutions or solvent-free substances at temperatures of preferably 20 to 100° C.
• the polymers of Formula I do not exhibit any organically bound halogen.
• halide ions are added to the polymers of the Formula I.
• the addition of halide ions may in this case occur by addition of the corresponding mineral acids, in particular hydrochloric acid, or by quaternization of the terminal tertiary amino functionalities with the corresponding alkyl halides or by addition of alkaline, earth alkaline, zinc or ammonium halides.
• ammonium halides alkyl ammonium halides may be used besides the unsubstituted ammonium halide, such as tetraalkylammonium chloride or ammonium salts, as described in U.S. Pat. No. 3,960,677.
• the polymer of the Formula I is acidified using hydrochloric acid.
• approx. 2 equivalents of hydrochloric acid per equivalent of polymer are added.
• the deposition results may be improved by addition of halide ions.
• the distribution of the electrolyte and the tendency towards burnings can be reduced.
• an increase of the current efficiency in the low current density area is achieved by addition of halide ions.
• halide ions a variation of the brightness level is possible.
• the polymers of Formula I can be produced selectively and reproducibly in accordance with the desired intended purpose.
• the possibility to build tailor-made block polymers is particularly advantageous. These may be consecutively built up by a targeted combination of various dimers, trimers or oligomers, respectively, by linkage with one or more dihalides.
• the polymers of the Formula I may be particularly built by consecutive linkage of different oligomer building blocks, such as dimers and/or trimers with one or more dihalides and pseudo halides of the Formula VIII in a segment-controlled manner.
• the polymers of the Formula I can be used in various zinc or zinc alloy baths, which are described in more detail in the following.
• the electrolyte bath according to the invention may thus be an acidic or alkaline zinc or zinc alloy bath.
• the electrolyte bath according to the invention is cyanide-free.
• the polymer of the Formula I is preferably contained in an amount of 0.01 to 50 g/L, preferably 0.25 to 10 g/L.
• the bath may contain a combination of various polymers of the Formula I.
• Cyanide-free zinc electrolytes and their alloy baths may be divided into two types, namely weakly acidic zinc electrolytes (containing zinc chloride and/or zinc sulfate, respectively) and alkaline zinc electrolytes.
• weakly acidic zinc electrolytes containing zinc chloride and/or zinc sulfate, respectively
• alkaline zinc electrolytes alkaline zinc electrolytes.
• a uniformly bright zinc layer is deposited from weakly acidic zinc bath, but these have the disadvantage that their current efficiency is always 100% over a broad current density range.
• this may be judged as advantageous, since the current is used up for zinc deposition exclusively, however, in case of work pieces which have a complex geometry, this leads to a thick zinc layer in the area of high current density and to very thin zinc layers in the area of low current density.
• the ratio of thickness of the zinc layer in the high current density range to the thickness of the zinc layer in the lower current density range is called layer thickness distribution (distribution coefficient) and is 1 in the ideal case. From the technical functional point of view, a zinc layer on the workpiece to be coated should have the same or approximately the same layer thickness at high brightness everywhere.
• Alkaline zinc electrodeposition baths are generally composed on the basis of an aqueous solution of zinc cations in the presence of alkali metal hydroxides.
• the documents DE 25 25 264 and U.S. Pat. No. 3,884,774 describe such electrolytes, however, the zinc layers obtained therewith do not show a uniform distribution of layer thickness.
• Such baths contain an inorganic alkaline component, preferably a hydroxide of an alkali metal, and especially preferably sodium hydroxide, potassium hydroxide and/or lithium hydroxide to adjust a pH value of at least 10, and preferably at least 11. In this case, amounts of 50 to about 250 g/L, and especially preferably 90 to 130 g/L of the alkaline component may be used.
• the electrolyte baths according to the invention usually contain zinc cations in concentrations which range from about 0.1 to about 100 g/L, wherein concentrations of 4 to 30 g/L are preferred.
• the zinc ion may be present in the bath according to the invention in the form of a soluble salt, for example zinc oxide, zinc sulfate, zinc carbonate, zinc acetate, zinc sulfamate, zinc hydroxide, or zinc tartrate.
• the bath according to the invention may contain about 0.1 to 50 g/L of metal ions.
• Suitable alloy metal salts are hydroxides, sulfates, carbonates, ammonium sulfates, sulfamates, acetates, formiates and halides, preferably chloride and bromide.
• the suitable alloy metals preferably cobalt, nickel, manganese and/or iron can be considered.
• the concentration of the alloy metal ions in the bath according to the invention may vary within a broad range and amounts to between 0.01 and 100 g/L. Since a different alloy content is required for different types of alloys in order to improve corrosion resistance, this concentration varies depending on the metal ions.
• the baths according to the invention may contain, as the alloy metal, from 0.1 to 50 g/L of nickel ions.
• Suitable nickel salts are nickel hydroxide, nickel sulfate, nickel carbonate, ammonium nickel sulfate, nickel sulfamate, nickel acetate, nickel formiate and nickel halides.
• the electrolyte bath contains zinc in an amount of 0.1 to 30 g/L and cobalt in an amount of 10 to 120 mg/L, nickel in an amount of 0.3 to 3 g/L, manganese in an amount of 10 to 100 g/L and/or iron in an amount of 10 mg/L to 30 g/L.
• pyridinium derivatives of e.g. nicotinic acid or nicotinamide, as described in U.S. Pat. No. 6,652,728, may be used.
• the baths according to the invention contain the aforementioned additional metal ions, it is appropriate to additionally add complexing agents to these baths which are compatible with these additional metal ions, in order to control the deposition potentials and in order to allow a co-reduction with the present zinc ions.
• chelating agents are preferred.
• suitable complexing agents are hydroxy carboxylates, such as sodium gluconate, amino alcohols such as triethanolamine, polyamines such as polyethylene diamine, aminocarboxylates such as EDTA or Trilon M, aminophosphonates such as amino-tris(methylenephosphonic acid), and polyvalent alcohols such as sorbitol or sucrose.
• the complexing agents may be contained individually or in a mixture in the baths according to the invention with the amounts being preferably in the range of 2 to 200 g/L.
• the baths according to the invention may contain levelling agents such as 3-mercapto-1,2,4-triazole and/or thiourea.
• concentration of the levelling agent corresponds to the usual concentration of zinc baths and amounts to e.g. 0.01 to 0.50 g/L.
• Further additives for the baths according to the invention are aromatic aldehydes or their bisulfite adducts.
• Preferred aromatic aldehydes are 4-hydroxybenzaldehyde, 4-hydroxy-3-methoxy-benzaldehyde, 3,4-dimethoxybenzaldehyde, 3,4-methylendioxybenzaldehyde, 2-hydroxybenzaldehyde and mixtures thereof.
• These additives which concentration is in the range of 0.005 to 1.0 g/L, preferably 0.01 to 0.50 g/L, act as brightening agents in a manner known per se.
• the baths according to the invention may contain, as a brightening agent, other substances as well, selected from the group of sulfur compounds, aldehydes, ketones, amines, polyvinyl alcohol, polyvinyl pyrrolidone, proteins or reaction products of halohydrines with aliphatic amines, polyamines or heterocyclic nitrogen compounds or mixtures thereof.
• the baths according to the invention may contain, in addition, water softening agents, which reduce the sensitivity of the electrolyte according to the invention towards foreign metal ions, in particular calcium and magnesium from tap water, using such additives.
• water softening agents are EDTA, sodium silicate and tartaric acid.
• the baths according to the invention effect the deposition of a blank, planar and ductile zinc or zinc alloy layer at any common temperature ranging from about 15° C. to 50° C., preferably 20° C. to 30° C., especially preferably about 25° C. At this temperatures, the baths according to the invention are stable and effective over a wide current density range of 0.01 to 10 A/dm 2 , particularly preferably 0.5 to 4 A/dm 2 .
• the polymers of Formula I surprisingly show particularly advantageous effects in case of alkaline zinc nickel deposition.
• the acidic bath according to the invention contains zinc ions in a concentration of about 0.2 to 80 g/L, preferably 10 to 50 g/L.
• the acidic zinc and zinc alloy electrolytes according to the invention may contain one or more salts for increasing the conductivity, such as sodium chloride, sodium sulfate, sodium fluoride, potassium chloride, potassium fluoride, potassium sulfate, ammonium chloride, ammonium fluoride and/or ammonium sulfate in an amount of 50 to 300 g/L or more.
• salts for increasing the conductivity such as sodium chloride, sodium sulfate, sodium fluoride, potassium chloride, potassium fluoride, potassium sulfate, ammonium chloride, ammonium fluoride and/or ammonium sulfate in an amount of 50 to 300 g/L or more.
• the tin-zinc electrolytes according to the invention may also contain one or more brightening agents known in the art.
• the baths contain at least one further brightening agent, selected from aromatic carbonyl compounds.
• the aromatic carbonyl compounds act as a brightening agent, which impart an optimum levelling and brightening effect over a wide range of current density.
• the aromatic carbonyl compounds may be aromatic aldehydes, acetophenones and carbonyl compounds.
• aromatic aldehydes examples include benzaldehyde, o-chlorobenzaldehyde, m-chlorobenzaldehyde, p-chlorobenzaldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, o-aminobenzaldehyde, veratraldehyde, 2,4-dichlorobenzaldehyde, 3,4-dichlorobenzaldehyde, 3,5-dichlorobenzaldehyde, 2,6-dichlorobenzaldehyde, tolualdehyde, 3,4-dimethoxybenzaldehyde, cinnamaldehyde, anisaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, 2-methoxy-1-naphthaldehyde, 2-hydroxy-1-naphthaldehyde, 2-ethoxy-1-
• naphthaldehyde with a benzaldehyde, for example 1-naphthaldehyde and 2,6-dichlorobenzaldehyde
• a superior deposition on the substrates is provided.
• carbonyl compounds include aromatic aldehydes and ketones such as benzylidene acetone, coumarin, acetophenone, propiophenone, and 3-methoxybenzacetophenone.
• Further carbonyl compounds include furfurylidene acetone, 3-indole carboxaldehyde and thiophene carboxaldehyde.
• the amount of the aromatic aldehyde for the carbonyl containing compounds in the baths according to the invention is in the range of up to about 2 g/L of bath and preferably from about 0.005 to about 2 g/L of bath.
• the brightening agents are generally added to the electroplating baths as the bisulfite addition products.
• mixtures of aliphatic aldehydes and the above-described aromatic aldehydes and mixtures of naphthaldehydes and benzaldehydes are also suitable.
• suitable combination include the following: a mixture of acid aldehyde and 4-methoxy-1-naphthaldehyde, a mixture of formaldehyde, 1-naphthaldehyde and 2,6-dichlorobenzaldehyde etc.
• carboxyl containing brightening agent compounds include the aromatic carboxylic acids and salts thereof, such as benzoic acid, sodium benzoate, sodium salicylate and nicotinic acid.
• the pH value of the acidic zinc and zinc alloy baths of the invention amounts to between 2 to 7, preferably 4 to 6.
• the baths according to the invention effect deposition of a blank, planar and ductile zinc or zinc alloy layer at each common temperature of about 15° C. to 60° C., preferably 20° C. to 45° C., particularly preferably about 25° C. to 40° C. At these temperatures, the baths according to the invention are stable and effective over a wide current density range of 0.01 to 20 A/dm 2 , preferably 0.1 to 15 A/dm 2 , and particularly preferably 0.1 to 10 A/dm 2 .
• the suitable alloy metals preferably cobalt, nickel, manganese, tin and/or iron are to be considered.
• the concentration of the alloy metal ions in the baths according to the invention may vary within wide range and amounts preferably to 0.01 to 300 g/L. As a different content of alloy is required for different alloy types, for example in order to improve the corrosion resistance, the concentration varies, depending on the metal ion.
• the acidic zinc nickel baths according to the invention contain, as the alloy metal, about 0.1 to 110 g/L, preferably 1 to 35 g/L of nickel ions.
• Suitable nickel salts are nickel sulfate, nickel carbonate, ammonium nickel sulfate, nickel sulfamate, nickel acetate, nickel formiate and nickel halides.
• the acidic zinc cobalt bath according to the invention contain, as the alloy metal, about 0.01 to 10 g/L of cobalt ions.
• the electrolytes according to the invention contain 10 to 60 g/L of iron ions.
• Suitable iron salts are iron sulfate, iron methane sulfonate, ammonium iron sulfate, iron sulfamate, iron acetate, iron formiate and iron halides.
• the electrolyte bath contains zinc in an amount of 0.1 to 30 g/L and cobalt in an amount of 10 mg to 120 mg/L, nickel in an amount of 0.3 to 3 g/L, manganese in an amount of 10 to 100 g/L and/or iron in an amount of 10 mg/L to 30 g/L.
• the polymers of the Formula I according to the invention may be used in acidic tin-zinc alloy baths.
• the tin-zinc alloy baths according to the invention contain between 0.1 to 10 g/L, particularly preferably 0.2 to 6 g/L of the polymer of Formula I.
• the tin-zinc electrolyte baths according to the present invention preferably contain tin(II) ions in concentrations of about 1 g/L to about 100 g/L and the zinc ions in a concentration of about 0.2 to 80 g/L.
• the electrolyte baths contain about 5 g/L to 40 g/L of tin(II) ions and about 5 to about 50 g/L of zinc ions.
• the range and the ratio limits may be combined and varied.
• the tin(II) ion may be present in form of a soluble salt, such as tin(II) sulfate, tin(II) methane sulfonate, tin(II) chloride, tin(II) fluoride, tin(II) sulfamate, tin(II) acetate, tin(II) oxide, etc.
• the zinc ion may exist in the bath in form of zinc sulfate, zinc methane sulfonate, zinc sulfamate, zinc chloride, zinc fluoride, zinc acetate, zinc tetrafluoro borate, etc.
• tin(II) ions as well as zinc ions are present in form of the chloride salts.
• the composition of the tin-zinc alloy deposition includes 0 to 100 wt.-% of tin, preferably 20 to 60 wt.-% of tin, and particularly preferably 30 to 50 wt.-% of tin.
• the tin-zinc alloy electrolyte may contain monomer salts for increasing the conductivity, such as sodium chloride, sodium sulfate, sodium fluoride, potassium chloride, potassium fluoride, potassium sulfate, ammonium chloride, ammonium fluoride and/or ammonium sulfate in an amount of 50 to 300 g/L or more.
• monomer salts for increasing the conductivity such as sodium chloride, sodium sulfate, sodium fluoride, potassium chloride, potassium fluoride, potassium sulfate, ammonium chloride, ammonium fluoride and/or ammonium sulfate in an amount of 50 to 300 g/L or more.
• the salt for increasing the conductivity are chlorides, and the tin(II) and zinc salts are tin(II) chloride and zinc chloride.
• the baths according to the invention contain the aforementioned additional metal ions, it is appropriate to additionally add complexing agents to these baths which are compatible with these additional metal ions, in order to control the deposition potentials and in order to allow a co-reduction with the present zinc ions.
• chelating agents are preferred.
• suitable complexing agents are hydroxy carboxylates, such as sodium gluconate, amino alcohols such as triethanolamine, polyamines such as polyethylene diamine, aminocarboxylates such as EDTA or Trilon M, aminophosphonates such as amino-tris(methylenephosphonic acid), and polyvalent alcohols such as sorbitol or sucrose.
• the complexing agents may be contained individually or in a mixture in the baths according to the invention with the amounts being preferably in the range of 2 to 200 g/L.
• the electrolyte baths according to the invention may be used for bulk parts, for example in drum electrodeposition methods and for deposition on larger workpieces in rack plating methods.
• anodes are used which may be soluble, such as zinc anodes, which serve, at the same time, as a source for zinc ions in order to substitute the zinc deposited on the cathode by dissolution of zinc at the anode.
• alloy depositions alloy anodes or anodes of the alloy metal, respectively, and/or two anodes, composed of tin and the alloy metal, may be used.
• unsoluble anodes e.g. platinised titanium mixed oxides
• the withdrawn zinc ion and/or further metal ions have to be re-added in case of alloy depositions, e.g. by using a zinc dissolving tank.
• the deposition method may be operated with injection of air, with movement of the articles or without movement without any disadvantages resulting for the obtained coatings.
• it may be worked using separation of electrode spaces, or by using membrane anodes, respectively.
• a electrolyte bath for electrodeposition of a zinc or zinc alloy layer according to claim 1 (1) A electrolyte bath for electrodeposition of a zinc or zinc alloy layer according to claim 1 .
• electrolyte bath according to one of paragraphs (1) to (7), wherein the electrolyte bath is an alkaline electrolyte bath and contains the further metal ions of cobalt, nickel, iron and/or manganese.
• electrolyte bath according to one of paragraphs (16) to (24), wherein the electrolyte bath contains one or more salts for increasing the conductivity, such as sodium chloride, sodium sulfate, sodium fluoride, potassium chloride, potassium fluoride, potassium sulfate, ammonium chloride, ammonium fluoride and/or ammonium sulfate.
• salts for increasing the conductivity such as sodium chloride, sodium sulfate, sodium fluoride, potassium chloride, potassium fluoride, potassium sulfate, ammonium chloride, ammonium fluoride and/or ammonium sulfate.
• a process for electrodeposition of bright and planar zinc or zinc alloy coatings comprising the steps of immersing a substrate to be coated into an electrolyte bath according to one of paragraphs (1) to (26).
• Table 1 shows the layer thickness (and thus current efficiency), brightness, burnings and layer thickness distribution regarding the electrolytes according to the invention for deposition of a zinc layer.
• the layer thickness distribution is the ratio of the layer thickness of the zinc layer in the high current density range (HCD) to the layer thickness in the low current density range (LCD), as shown in Table 1.
• the ratio having the value of 2.6 is with respect to Example 9 (prior art) the worst, whilst it amounts, using the additives according to the invention, to between 1.38 (Example 8) and 2.0 (Example 1).
• the burnings in the high current density range are weaker, or do not exist anymore, respectively.
• the polymers must not or may not, respectively, have a higher degree of polymerization.
• the halide ions may be in form of the corresponding mineral acids, or by quaternization of the terminal tertiary amino functionalities using the corresponding alkyl halides, or by addition of alkali metal, earth alkali metal, zinc or ammonium halides, respectively.
• ammonium halides besides the unsubstituted ammonium halide, also alkyl ammonium halides such as tetraalkylammoniumchloride or ammonium salts, e.g. as described in U.S. Pat. No. 3,960,677, may be used.
• Table 3 emphasizes the effect of the electrolyte compositions according to the present invention for zinc-nickel depositions. As can be seen from Table 3, a bright and uniform deposition can be obtained over the whole current density range. Using the known polymers Mirapol WTTM (Example 13), homogenous glossy layers are merely obtainable in high to middle current density ranges.
• Table 4 emphasizes that the burnings often occurring in conventional acidic zinc baths can be avoided by the polymer of the Formula I. As can be seen from Table 4, more glossy zinc depositions can be obtained with the polymers of the Formula I from weakly acidic ammonium containing baths than by using commercially available polymers. By addition of halides, e.g. in the form of hydrochloric acid, an improvement of the layer can be achieved (cf. Examples 14 and 15: higher gloss using a composition according to Example 15 containing chloride).

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